GLACIAL DRIFTS IN MINNESOTA 
383 
GLACIAL DRIFT SHEETS IN MINNESOTA 
By Dr. Frederick W. Sardeson 
Minneapolis, Minnesota 
It has taken fifty years for geologists to bring our knowledge 
of glacial drift to.such a condition that the Pleistocene Glacial 
history of Minnesota may be described in terms that are concise 
and simple enough to be of interest to all. Recent field-work by 
Frank Leverett, the results of which are already published in 
part, leaves few problems in Minnesota not solved and simplified. 
The evidence of glaciers in the state is complex. A small part of 
the area, or less than one per cent of the surface, is not, or has 
not at any time been, covered by Glacial drift. That small part 
lies in the extreme southeast corner, and belongs to the so-called 
Driftless Area. 
This Driftless Area lies mainly in Wisconsin, and is so called 
because of the fact that it is completely surrounded by areas of 
bouldery drift, but is itself free from all drifted materials, ex¬ 
cepting those of gravel and sand swept down by the rivers, and 
sand or dust deposits swept from the valleys by the winds onto the 
hills. Aside from the Driftless Area, the surface of Minnesota 
has been covered by glaciers one or more times, and has from 
one to two, three of four bouldery drift-sheets in evidence of 
them in different parts. 
The last time or stage of Glacial action in Minnesota covered 
also the greater part of the State as shown on the accompanying 
sketch (plate xxxiv), so that the evidences of former stages 
have to be described in part from drift remnants that lie under 
this last complex of drift materials. Early drift stages, however, 
had wider glaciation even than this last one, so that some surface 
area lies within the boundaries of Minnesota. 
